You are making that assumption. Federal retirement benefits are part of the total costs and benefits for an employee.
I ran a consulting company; when you are competing against the government employees to determine if a project will be outsourced, you were required to add in all costs, and so were the feds. The end result, I got to see the costs in detail. No matter if I used BLS data from DOL, or looked at the pure numbers from GSA, or even from the agency. What matters in all cases, is the loaded cost. And for the feds, that includes retirement.
Tim